Interface engineering to achieve long-term stability of ultra-thin silver film on silica

Abstract

We report zinc (Zn) as a seed layer material and a need for a specific deposition sequence to grow ultrathin silver (Ag) films on quartz (SiO₂). Ag films of thickness 4, 6, 8 and 10 nm were deposited by DC magnetron sputtering without and with Zn seed layer thickness of 1, 2 and 4 nm. The effect of Zn seed layer thickness and its annealing on the surface morphology, sheet resistance, and stability of ultrathin Ag films is investigated. We show that by increasing Zn seed layer thickness from 1 to 2 nm, there is a 5-order reduction in sheet resistance of 6 nm Ag films. We find that annealing of seed layer is crucial to achieve stability of ultrathin Ag films. 6 nm Ag film with 2 nm Zn is unstable to 100 °C annealing, while the 6 nm Ag film with annealed 2 nm Zn seed layer is stable. 2 nm Zn seeded 8 nm Ag film maintained a constant sheet resistance of 7 Ω/□ for all 6 months of exposure to ambient conditions. Such stable exposed ultrathin Ag films can find applications as catalysts, sensors, transparent conductive electrodes for solar cells, LEDs and plasmonic devices.